Although there has been significant progress in the investigation of the genetic basis of hypertension, much work remains to be done against the cumulative backdrop of persistent clinical mandates. In essence, essential hypertension remains a highly prevalent disease and remains a major risk factor for the top causes of mortality in the USA: coronary artery disease, heart failure, arrhythmias. stroke and renal disease. It has become clear that (1) gene interaction must be factored into the genetic analysis of complex genetic diseases, (e.g., essential hypertension); and that (2) gene interaction analysis in well-controlled animal model experiments coupled to prioritized subsequent testing in genetically isolated human populations provides a robust experimental strategy. These realizations along with insights, observations, as well as experimental approach validation obtained in the previous research proposal, provide us with the clinical and scientific mandates to investigate the following hypothesis: The unidirectional gene interaction of a1 Na,K-ATPase (a1NK) and Na,K,2C1-cotransporter (NKC) genes increasing susceptibility to hypertension identified in Dahl S rats by an intercross linkage analysis reflects an in vivo molecular interdependence of these transporters and as such it should be amenable to in vivo testing via strategic transgenic experiments. Accordingly, the following specific aims are prioritized for this continuing research proposal: Aim I: Determine the in vivo biological significance of the genetic correlation of the renal-specific Na,K,2Cl-cotransporter gene with hypertension in Dahl S rats. Aim II: Determine the in vivo biological significance of the statistical interactive correlation of a1NK and NKC genes on salt-sensitive hypertension by developing dual transgenic (bigenic) Tg[Ra 1NK x nkc-F)] and Tg[Ra 1NK x nkc-A)] Dahl S rats. The successful completion of this research program will define a) the alNa,K-ATPase and the bumetanide-sensitive Na,K,2Cl-cotransporter as bona fide hypertension susceptibility genes in Dahl S rats; and b) will pave the way for the direct assessment of the role of these genes in hypertension susceptibility in different human populations.